// 求返回字符串的字节数
let a = 'a',
    b='中',
    c= 'hello world'
let str='hello你好123';
    // 文件 -> blob -> 二进制
    // Blob 是什么
const byteSize=str=>new Blob([str]).size;    // html5
console.log(byteSize(a));
console.log(byteSize(b));
console.log(byteSize(c));
console.log(byteSize(str));
console.log(new Blob([str,c]));